Process for molnupiravir

ABSTRACT

The present invention relates to a process for the preparation of Molnupiravir. The present invention also relates to an improved and commercially viable process for preparation of Molnupiravir with high yield and purity.

CROSS REFERENCE TO RELATED APPLICATIONS

The instant application claims priority to the Indian provisionalapplication number 202141011933, filed on Mar. 20, 2021, the disclosureof all of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a process for the preparation ofMolnupiravir. The present invention also relates to an improved andcommercially viable process for preparation of Molnupiravir with highyield and purity.

BACKGROUND OF THE INVENTION

Molnupiravir (development codes MK-4482 and EIDD-2801) is anexperimental antiviral drug which is orally active and was developed forthe treatment of influenza. It is a prodrug of the synthetic nucleosidederivative N4-hydroxycytidine and exerts its antiviral action throughintroduction of copying errors during viral RNA replication. Activityhas also been demonstrated against coronaviruses including SARS, MERSand SARS-CoV-2.

In April 2020, a whistle blower complaint by former Head of USBiomedical Advanced Research and Development Authority (BARDA) RickBright revealed concerns over providing funding for the furtherdevelopment of Molnupiravir due to similar drugs having mutagenicproperties (producing birth defects). A previous company, Pharmasset,that had investigated the drug's active ingredient had abandoned it.These claims were denied by George Painter, CEO of DRIVE (DrugInnovation Ventures at Emory), noting that toxicity studies onMolnupiravir had been carried out and data provided to regulators in theUS and UK, who permitted safety studies in humans to move forward in thespring of 2020. Also at this time, DRIVE and Ridgeback Biotherapeuticsstated they planned future safety studies in animals.

After being found to be active against SARS-CoV-2 in March 2020,Molnupiravir was tested in a preliminary human study for “Safety,Tolerability, and Pharmacokinetics” in healthy volunteers in the UK andUS. In June 2020, Ridgeback Biotherapeutics announced it was moving toPhase II trials to test the efficacy of the drug as a treatment forCOVID-19. Two trials of small numbers of hospitalized andnon-hospitalized patients in the US and the UK were underway in July. Inlate July 2020, and without yet releasing any medical data, Merck, whichhad been partnering with Ridgeback Biotherapeutics on developing thedrug, announced its intention to move Molnupiravir to late-stage trialsbeginning in September 2020. On Oct. 19, 2020, Merck began a one-yearStage 2/3 trial focused on hospitalized patients.

The study found that the drug was “efficacious” when administered orallyto infected ferrets, and that it blocked the transmission of the virusbetween ferrets after 24 hours following administration of the drug.Molnupiravir structural formula is as follows:

Molnupiravir is reported in US 20200276219 (“US'219”) assigned to EmoryUniversity. The synthetic process for Molnupiravir is reported in US'219comprises reacting Uridine (VI) with acetone in presence of H₂SO₄/TEA toobtain the compound of formula (VII). The compound of formula (VII) isreacted with 2-methylpropanoyl 2-methyl propanoate in presence ofTEA/4-DMAP and EtOAc to obtain the compound of formula (VIII). Thecompound of formula (VIII) is reacted with 1,2,4-triazole in presence ofMeCN/N,N-diethylethanamine/POCl₃/H₂O and MDC to obtain the compound offormula (IX). The compound of formula (IX) is reacted with NH₂OH inpresence of IPA/EtOAc and H₂O to obtain the compound of formula (V). Thecompound of formula (V) deprotected with HCOOH in presence of MTBE/IPAto obtain Molnupiravir (I).

The above process is schematically shown as below:

Gopalsamuthiram et al. (“A Concise Route to MK-4482 (EIDD-2801) fromCytidine: Part 2” Synlett (2021), 32(3), 326-328) discloses a processfor the preparation of Molnupiravir (I), wherein Cytidine (II) isreacted with 2,2-dimethoxypropane in presence of acetone and H₂SO₄ toobtain 2′,3′-O-(1-methylethylidene)-sulfate Cytidine (III). The compoundof formula (III) is reacted with isobutyric anhydride in presence ofDBU/DMAP/MeCN/EtOAc/H₂O and sodium bicarbonate to obtain2′,3′-O-(1-methylethylidene)-5′-(2-methyl propanoate) Cytidine (IV). Thecompound of formula (IV) is reacted with NH₂OH.H₂SO₄ in presence ofIPA/H₂O/EtOAc/NaHCO₃ and toluene to obtain2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate) Uridine(V). The compound of formula (V) deprotected with HCO₂H to obtainMolnupiravir (I).

The above process is schematically shown as below:

The main drawback of the prior art is that the processes for thepreparation of Molnupiravir described thus far are associated with lowyield and low purity. Further, the processes described in the prior artrequire conversion of 2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methylpropanoate) Uridine (V) to crude Molnupiravir in presence formic acid(HCO₂H). Furthermore, the processes include a step of purifying crudecompound of Molnupiravir using silica gel column chromatography in 8%MeOH/CHCl₃ to obtain Molnupiravir (I). Hence, the number of stepsrequires various techniques to get a purified compound and with lessyield and purity.

The advantage of the present invention is process for the preparation ofMolnupiravir with high yield and high purity. In view of the foregoing,the present invention provides as result of extensive studies, processfor the preparation of Molnupiravir (I) from2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate) Uridine(V) in presence of trifluoroacetic acid or hydrochloric acid in suitableorganic solvents and temperatures.

SUMMARY OF THE INVENTION

The present invention relates to a process for the preparation ofMolnupiravir. The present invention also relates to an improved andcommercially viable process for preparation of Molnupiravir with highyield and purity.

The present invention provides a process for the preparation ofMolnupiravir (I), comprising the steps of,

-   -   a) reacting Cytidine (II) with 2,2-dimethoxypropane and H₂SO₄ in        presence of an organic solvent to obtain compound (III),        2′,3′-O-(1-methylethylidene)-sulfate Cytidine,

-   -   b) reacting compound (III) with isobutyric anhydride in presence        of an organic base and an organic solvent at a temperature of        0-5° C. for 60 min, to obtain compound (IV),        2′,3′-O-(1-methylethylidene)-5′-(2-methyl propanoate) Cytidine,

-   -   c) reacting compound (IV) with hydroxylamine sulfate in presence        of an organic solvent to obtain compound (V),        2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate)        Uridine,

-   -   d) deprotecting compound (V) with trifluoroacetic acid or        hydrochloric acid in presence of an organic solvent and water,        at a temperature of 50-55° C. for about 2-3 hours, to obtain        Molnupiravir (I), and

-   -   e) isolating Molnupiravir (I).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for the preparation ofMolnupiravir. The present invention also relates to an improved andcommercially viable process for preparation of Molnupiravir with highyield and purity.

The present invention provides a process for the preparation ofMolnupiravir (I), comprising the steps of,

-   -   a) reacting Cytidine (II) with 2,2-dimethoxypropane and H₂SO₄ in        presence of an organic solvent to obtain the compound (III),        2′,3′-O-(1-methylethylidene)-sulfate Cytidine,    -   b) reacting compound (III) with isobutyric anhydride in presence        of an organic base and an organic solvent at a temperature of        0-5° C. for 60 min, to obtain compound (IV)        2′,3′-O-(1-methylethylidene)-5′-(2-methyl propanoate) Cytidine,    -   c) reacting the compound of formula (IV) with hydroxylamine        sulfate in presence of an organic solvent to obtain compound        (V), 2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl        propanoate) Uridine,    -   d) deprotecting compound (V) with trifluoroacetic acid or        hydrochloric acid in presence of an organic solvent and water,        at a temperature of 50-55° C. for about 2-3 hours, to obtain        Molnupiravir (I), and    -   e) Isolating Molnupiravir (I).

In an embodiment of the present invention, Cytidine (II) is reacted with2,2-dimethoxypropane and H₂SO₄ in presence of acetone to obtain compound(III), 2′,3′-O-(1-methylethylidene)-sulfate Cytidine. In one aspect ofthe embodiment, compound (III) is reacted with isobutyric anhydride inpresence of DBU/DMAP/acetonitrile at 0-5° C. for 60 min to obtaincompound (IV), 2′,3′-O-(1-methylethylidene)-5′-(2-methyl propanoate)Cytidine. In another aspect of the embodiment, compound (IV) is reactedwith hydroxylamine sulfate in presence of isopropyl alcohol and water byKarl Fisher titration at 70-80° C. for 17-18 hours to obtain compound(V), 2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate)Uridine. In another aspect of the embodiment, compound (V) isdeprotected with trifluoroacetic acid or hydrochloric acid in presenceof an organic solvent and water at 25-60° C. for 2-3 hours, preferably50-55° is maintained for about 2-3 hours, wherein the reaction mass pHis maintained between 7.0-10.0 by using sodium carbonate solution toobtain Molnupiravir (I).

In another aspect of the embodiment, the amount of isobutyric anhydrideused in the range of about 0.05 to 1 mole, more preferably 0.55 to 0.57moles; the amount of DBU used in the range of about 0.5 to 1.5 moles,more preferably 1.06 to 1.16 moles; the amount of DMAP used in the rangeof about 0.01 to 1 mole, more preferably 0.07 to 0.10 moles In anotherembodiment, the instant application provides purification process forthe preparation of Molnupiravir (I), comprising the Molnupiravirpurified with organic solvent and the reaction is carried out at 70-80°C. for 10-15 min to obtain pure Molnupiravir (I).

According to one embodiment the Molnupiravir (I) obtained using aprocess described herein is ≥99.5% pure, measured using HPLC.

According to another embodiment of the present invention, the organicsolvent is selected from the group consisting of acetone, acetonitrile,ethyl acetate, water, isopropyl alcohol, methanol, ethanol, toluene,dimethyl sulfoxide (DMSO), dimethylformamide (DMF), isopropyl acetateand n-butyl acetate, methyl ethyl ketone, methyl isobutyl ketone,cyclohexanone, diethyl ether, di isopropyl ether, dioxane,tetrahydrofuran, 1,2-dimethoxyethane, dichloromethane (MDC),dichloroethane, carbon tetrachloride and chloroform and/or mixturesthereof.

According to yet another embodiment of the present invention, theorganic base is selected from 1,8-diazabicyclo [5.4.0] undec-7-ene(DBU), Dimethyl aminopyridine (DMAP), 5-diazabi cyclo[4.3.0]non-5-ene(DBN), pyridine, triethylamine (TEA), Diisopropylethylamine (DIPEA),trimethylamine, diethylamine and N,N-dimethylaniline.

The following examples illustrate the present invention but should notbe construed as limiting the scope of the invention.

EXAMPLES Example-1: Preparation of 2′,3′-O-(1-methylethylidene)-sulfateCytidine (III)

Acetone (100 ml), cytidine (10 gm) and 2,2-dimethoxypropane (30 ml) wereadded into RB (round bottom) Flask, followed by addition of sulphuricacid (4 ml) into flask at below 30° C., stir the mass at 25-30° C. for4-5 hours. After completion of the reaction, filter the resultant solidmaterial, wash with acetone (30 ml) and dry for 20 min. The obtainedcrude wet material into RB Flask, added ethyl acetate (70 ml) and Stirthe mass for 60 min at 25-30° C. The resultant solid was washed withethyl acetate (30 ml) and dry for 20 min. to get off white colourcompound.

Yield: 30 gms

Purity: 99.02%

Example-2: Preparation of 2′,3′-O-(1-methylethylidene)-5′-(2-methylpropanoate) Cytidine (IV)

Charge acetonitrile (75.0 ml), 2′,3′-O-(1-methylethylidene)-sulfatecytidine (30.0 gm) and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) (12.75ml) into RB flask at 25-30° C. Stir the reaction mass for 10 min to geta clear solution, further added 4-Dimethylamino pyridine (DMAP) (0.75gm) into flask, cool the mass to 0-5° C., slowly add isobutyricanhydride (6.9 ml) to the reaction mass at 0-5° C. and stir for 60 min.After completion of the reaction, charge purified water (150 ml) anddichloromethane (105 ml) to the reaction mass, Stir for 10 min toseparate the layers, extracted dichloromethane layer was washed with 10%sodium bicarbonate solution (30 ml). The separated organic layer (MDCLayer) was concentrated under reduced pressure at below 50° C. to gettitle compound.

Yield: 95.17% (13.8 gms)

Purity: 92.73%

Example-3: Preparation of2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate) Uridine(V)

Charge isopropyl alcohol (145 ml), purified water (41.4 ml),2′,3′-O-(1-methylethylidene)-5′-(2-methyl propanoate) Cytidine (13.8 gm)and hydroxylamine sulphate (17.25 gm) into RB flask at 25-30° C. Thereaction mass temperature raised to 70-80° C. and maintain for 17-18hours. After completion of the reaction, concentrate the mass underreduced pressure at below 70° C. and allow to cool at below 30° C.Charge purified water (138 ml) and 10% sodium carbonate solution intoflask, stir for 60 min. The obtain material was filtered, wash withpurified water (27.6 ml) and suck dry for 10 min, followed by additionof toluene (13.8 ml) and the reaction mixture was allowed to cool at0-5° C. and stir for 30 min. The resultant material was filtered, washedwith toluene (2.76 ml) and dry the material for 8 hours at 55-60° C. toget off white colour solid compound.

Yield: 80.12% (11.5 gm)

Purity: 96.81%

Example-4: Preparation of Molnupiravir (I)

2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate), Uridine(10 gm) and purified water (10 ml) were added into RB flask at roomtemperature, followed by addition of trifluoroacetic acid (30 ml) atbelow 35° C. The reaction mass was allow to stir for 2 hours at 50-55°C. After completion of the reaction, the reaction mass was concentratedunder reduced pressure at below 55° C. and allow to cool the mass at25-30° C., Quench the reaction mass with 30% sodium carbonate solution(50 ml) at same temperature and stir for 60-120 min, further cool to0-5° C. and stir for 20-30 min. The resultant material was filtered,washed with purified water (2 ml), ethyl acetate (5 ml) and dry thematerial at 60-65° C. to get Molnupiravir.

Yield: 69.66% (6.2 gms)

Purity: 97.79%

Example-5: Preparation of Molnupiravir (I)

Charge Ethyl acetate (100 ml),2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate) Uridine(10.0 gm) and purified water (1.0 ml) into RBF, followed by addition ofhydrochloric acid (2.70 gm) at 25-30° C. and allow to stir at 50-55° C.for 2-3 hours. After completion of the reaction, Cool the masstemperature to 25-30° C., adjust the reaction mass pH to 7.5-8.5 with10% Sodium carbonate solution (50.0 ml) and stir for 15-20 min toseparate the two layers. The obtain ethyl acetate layer was wash with30% sodium chloride solution and water (20 ml), further it was chargedwith activated carbon (0.2 gm), stir for 10-15 min at room temperatureand filter the mass through hyflo bed. The filtrate (ethyl acetatelayer) was concentrated under vacuum at below 60° C. under reducedpressure and degas the mass at the same temperature under vacuum for 60min. The resultant material was washed with ethyl acetate (10.0 ml) anddried at 60-65° C. for 8-10 hours to obtain 7.50 gm of the purematerial.

Yield: 84.26% (7.50 gm)

Purity: 99.9%

Example-6: Purification of Molnupiravir

Crude Molnupiravir material (91.0 gm) were added to isopropyl alcohol(600 ml), stir the mass at 70-80° C. for 10-15 min to dissolve thematerial. Charge activated carbon (5.0 gm) and stir for 10 min at thesame temperature. The reaction mass was filter through hyflo bed andwash with isopropyl alcohol (100 ml). The reaction mass was concentratedunder reduced pressure at below 60° C., further added purified water(200 ml) and stir for 10-15 min at 60-65° C. The reaction mass was allowto 0-5° C. and stir for 30-60 min at the same temperature. The resultantmaterial was filter, washed with chilled purified water (25 ml) anddried at 60-65° C. to get pure Molnupiravir.

Yield: 68.08% (60.6 gm)

Purity: 99.79%.

We claim:
 1. A process for preparation of Molnupiravir (I), comprising:a) reacting Cytidine (II) with 2,2-dimethoxypropane and H₂SO₄ inpresence of organic solvent to obtain compound (III),2′,3′-O-(1-methylethylidene)-sulfate Cytidine,

b) reacting compound (III) with isobutyric anhydride in presence oforganic base and organic solvent, at a temperature of 0-5° C. for 60min, to obtain compound (IV), 2′,3′-O-(1-methylethylidene)-5′-(2-methylpropanoate) Cytidine,

c) reacting compound (IV) with hydroxylamine sulfate in presence oforganic solvent to obtain compound (V),2′,3′-O-(1-methylethylidene)-4-oxime-5′-(2-methyl propanoate) Uridine,

d) deprotecting formula (V) with trifluoroacetic acid or hydrochloricacid in presence of organic solvent and water, at a temperature of50-55° C. for about 2-3 hours, to obtain Molnupiravir (I), and

e) isolating the Molnupiravir (I).
 2. The process according to claim 1,wherein the organic solvent in step a) is acetone, step b) isacetonitrile, step c) is isopropyl alcohol, and step d) is ethylacetate.
 3. The process according to claim 1, wherein the organic baseis selected from the group consisting of 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU), Dimethylaminopyridine (DMAP), 5-diazabicyclo[4.3.0]non-5-ene (DBN), pyridine, triethylamine (TEA),Diisopropylethylamine (DIPEA), trimethylamine, diethylamine andN,N-dimethylaniline.